Insulating glass units ("IGUs"), made with at least two glass panels arranged in spaced-apart relationship with an edge assembly to form an enclosed interior space, require the presence of a desiccant in the interior space to avoid condensation of moisture or other volatile materials due to the temperature difference between the inner and outer glass panels. Such condensation is generally referred to as "fogging" of the IGU. Moisture or materials such as volatile organic chemicals ("VOCs") may remain in the interior space after manufacture or may seep into the interior space during post-manufacture use. The moisture and VOCs may cause fogging in the interior space. The desiccant is provided to remove the moisture and/or VOCs from the interior space by adsorption. As used hereinafter, the terms "desiccating materials" and "desiccants" include adsorbents of both moisture and VOCs, except where specific adsorbents of moisture or VOCs are separately identified and limited as to specific materials adsorbed.
In early IGUs, loose particles of desiccating materials in a container were placed in the interior space of the IGU, free of any matrix for holding together the desiccant particles. This resulted in problems such as spillage of the desiccating material from the spacer, bead migration and dusting, too-rapid adsorption of moisture resulting in premature saturation of the desiccant prior to assembly of the IGU and reduced life expectancy or premature failure of the IGU, and included problems in manufacture due to the size and nature of the particles of desiccant materials. An early example of such units may be found, for example, in U.S. Pat. No. 2,964,809. Similarly, in later IGUs, the loose desiccant material was disposed in the body of the spacer itself, such as is shown in U.S. Pat. No. 3,998,680.
Later IGUs were provided with a desiccant dispersed within a thermoplastic carrier, in which the thermoplastic was placed in the interior space, as shown, for example in U.S. Pat. No. 3,758,996. In an effort to simplify construction of the IGU, dimensionally stable sealant and spacer strips were developed. Such strips include an elongated ribbon of deformable sealant having an imbedded spacer means such as a corrugated metal strip. On the inner side of this strip is disposed a decorative facing which has impregnated therein a desiccant. Such a system is sold as SWIGGLE.RTM. Seal, and is disclosed in U.S. Pat. No. 4,431,691. Other IGUs include a spacer made of silicone or acrylic foam containing large quantities of a desiccant fill material, such as is shown in U.S. Pat. No. 4,950,344. An IGU with a spacer filled with a desiccating matrix is disclosed in U.S. Pat. No. 5,209,034.
Among other developments in this area are insulating glass units such as those shown in U.S. Pat. No. 5,177,916 and the progeny thereof, in which a U-shaped spacer is placed between glass panels to form an interior space, and an adhesive containing a desiccant is coated on the inside of the U-shaped spacer. A drawback of using mastics in an IGU like that described in U.S. Pat. No. 5,177,916 arises from limitations imposed by the mastic. The material may soften such that it sags at the temperatures to which the IGU is exposed in use. The desiccating mastic may evolve an excessive amount of water or organic vapors, which can result in fogging. Thus, two-part, curing formulations have been avoided, since curing reactions may evolve volatile byproducts. The mastic should be UV stable, since it will be directly exposed to UV radiation throughout its useful life. U.S. Pat. No. 5,510,416 describes a particular hot melt thermoplastic mastic. The hot melt mastic of U.S. Pat. No. 5,510,416 forms a coating on the interior of the U-shaped spacer of the IGU, so as to be retained thereon, to avoid the problem of sagging and to prevent separation of the hot melt mastic from the spacer.
Another approach to providing desiccating materials in the interior space of IGUs is the DESI-ROPES.RTM. continuous desiccating cord. Such cord is provided in continuous, pre-extruded lengths, for insertion into the spacer during manufacture of the IGU. The DESI-ROPE.RTM. is believed to be a cured EPDM elastomeric material impregnated with a desiccant. This product avoids some of the problems associated with the thermoplastic compositions, but comes with its own set of drawbacks. Since the cord is pre-manufactured and contains desiccant, it must be handled and stored appropriately between the times of manufacture and use so as to avoid premature moisture adsorption and saturation. According to the manufacturer's information, reels of the DESI-ROPE.RTM. material are supplied in vacuum-sealed, moisture-proof foil bags which are in turn packaged in high density polyethylene bags, and shipped in cardboard boxes. As a result, packaging for protecting this product from inadvertent exposure to moisture is an important issue, resulting in additional costs and handling and storage precautions.